A variable capacitor is an important part in electrical circuits such as a variable frequency oscillator, tuned amplifier, phase shifter, impedance-matching circuit and the like, and in recent years, use in portable devices has been increasing. In comparison with varactor diodes that are mainly used now, variable capacitors that are manufactured using MEMS technology have the advantage of less loss and higher Q value, therefore development is rapidly advancing.
FIG. 1(a) is a cross-sectional view and FIG. 1(b) is a top view showing the construction of a conventional variable capacitor (for example, refer to non-patent document 1). This variable capacitor is constructed so that a movable electrode substrate 11, having a unimorph-type piezoelectric actuator 12 and movable electrode 13, and a stationary electrode substrate 15, on which a stationary electrode 16 is mounted, are joined using solder bumps 14, so that the movable electrode 13 and stationary electrode 16 face each other. The piezoelectric actuator 12 drives and moves the movable electrode 13, and the capacity of the capacitor is controlled by varying the distance between the movable electrode 13 and stationary electrode 16.
[Non-patent Document 1]
Jan Y. Park, et al., “MICROMACHINED RF MEMS TUNABLE CAPACITORS USING PIEZOELECTRIC ACTUATORS”, IEEE International Microwave Symposium, 2001